Running Bootcamp

Ok so I've done some reading up and I seem to be the only on in the world that can't get my bootcamp working on my mac.
When I run bootcamp assistant and try to 'Download the latest Windows support software from Apple' this appears: USB drive can not be used 'Please format the USB drive as single FAT partition.' Now I read I should "Open Disk Utility, select the USB drive in the list, click Erase tab, make sure Format is set to FAT, click Erase button." The only format options I see with "FAT" in it is MS-DOS (FAT) and ExFAT. I have no idea what to do at this point. (FYI: I'm using FreeAgent GoFlex Drive 500GB with about 240GB used by the back up I just completed.) Will going through all this get me passed this issue so I can download and install windows? I would greatly appreciate a step by step explanation. I've only been a Mac user for a little over a year and only realize now that I know nothing about them.
Everyone explains the Bootcamp setup as this simple process but it hasn't been that way on my end.